During pregnancy small numbers of fetal erythrocytes enter the maternal circulation. Among these cells are nucleated erythrocytes called normoblasts. Genomic analysis of these normoblasts using specific probes by in situ hybridization or the polymerase chain reaction (PCR) potentially provides a non-invasive method for diagnosis of genetic defects. Because the number of fetal normoblasts among the maternal cells is extremely low, a series of encrichment steps is required to obtain a homogeneous population of fetal cells. We have developed methods for obtaining fetal normoblasts using a flow cytometric approach. We have also determined conditions for performing PCR on genomic DNA prepared from as little as 50 cells. The goals of this proposal are: 1) to devise techniques for isolating a pure population of fetal normoblasts from a small sample of maternal blood and 2) to use the enriched normoblast from a small sample of maternal blood and 2) to use the enriched normoblast population for detecting single copy genes. Controls for contaminating maternal genomic DNA will be incorporated into the study based on highly polymorphic repeat sequences including a "TG" repeat sequence we discovered on human chromosome 7. Phase II will focus on prenatal diagnosis of specific genetic disorders such as sickle cell anaemia and thalassaemia. PROPOSED COMMERCIAL APPLICATION: We intend to devise a non-invasive method for prenatal diagnosis of genetics defects. In addition to reducing the risk to the fetus, our sampling method has the potential for automated processing of samples in a commercial diagnostic laboratory.